Venezuelan equine encephalitis in Panama: fatal endemic disease and genetic diversity of etiologic viral strains.
Bottom Line: Recent clusters of cases occurred in Darien (eastern Panama) and Panama provinces (central Panama) near rainforest and swamp habitats.Patients ranged from 10 months to 48 years of age, and the more severe cases with neurological complications, including one fatal infection, were observed in children.These findings underscore endemic VEE as an important but usually neglected arboviral disease of Latin America.
Affiliation: Gorgas Memorial Institute, Panama City, Panama.
Venezuelan equine encephalitis (VEE) is a reemerging, mosquito-borne viral disease of the neotropics that is severely debilitating and sometimes fatal to humans. Periodic epidemics mediated by equine amplification have been recognized since the 1920s, but interepidemic disease is rarely recognized. We report here clinical findings and genetic characterization of 42 cases of endemic VEE detected in Panama from 1961-2004. Recent clusters of cases occurred in Darien (eastern Panama) and Panama provinces (central Panama) near rainforest and swamp habitats. Patients ranged from 10 months to 48 years of age, and the more severe cases with neurological complications, including one fatal infection, were observed in children. The VEE virus strains isolated from these cases all belonged to an enzootic, subtype ID lineage known to circulate among sylvatic vectors and rodent reservoir hosts in Panama and Peru. These findings underscore endemic VEE as an important but usually neglected arboviral disease of Latin America.
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Mentions: To investigate genetic relationships among the VEEV strains from Panama in comparison to others isolated from different regions of the Americas, phylogenetic analyses were performed. Maximum parsimony, neighbor joining and Bayesian methods all generated similar tree topologies. The neighbor-joining tree based on the partial PE2 sequences (Figure 2) showed that most of the subtype ID VEEV strains from Panama formed a single clade, with previously sequenced Panamanian subtype ID strains as well as some Peruvian ID isolates. This group was previously called the Panama-Peru subtype ID genotype . Within this group, 2 distinct clades among the Panamanian strains were observed: 1) strains from Central Panama; 2) isolates from Eastern Panama (Darien). The final subtype ID isolate, strain 213391 from western Panama (Bocas del Toro Province), was phylogenetically distinct from all other ID isolates. Our phylogenies placed it outside of the Panama/Peru genotype, but this placement was supported by a bootstrap value of only 69%. The location of collection of this strain was geographically close to those of subtype IE strains isolated in the 1960s (Fig. 2). Therefore, the geographic ranges of subtypes ID and IE may overlap slightly.